(a) Field of the invention
The present invention relates to a reproducing objective for video disks.
(b) Description of the prior art
For reproduction of signals recorded on a video disk, the method to make the objective perform fine oscillation is often adopted in order to correct the tracking error as well as the method to oscillates a galvano-mirror. In this method, the objective performs fine oscillation of about 10 to 90 Hz. Therefore, the objective should be small in size and light in weight as far as possible. Besides, the objective should be located at least at a certain distance from the video disk surface. Otherwise, the objective will contact the disk surface in actual use and will cause damage to the disk. Therefore, the objective for video disks should have a long working distance.
However, in case of known objective for video disks comprising lenses made of optical glass, it is impossible to satisfy the requirements to make the objective small in size and light in weight though it is possible to make the working distance long. Especially, the requirement to make the objective small in size is not satisfied. To solve the above-mentioned problem, objectives for video disks comprising lenses made of plastics (plastic lenses) are also known. However, in case of those objectives, the working distance is short and insufficient and, moreover, the resolving power is lower compared with objectives for video disks comprising lenses made of optical glass though it is possible to make the objective satisfactorily light in weight.